Preview
Video Player
00:00
00:00
The Solution
4:07Now that you've coded your solution to the practice problem, I'll show you how I did it.
Your goal was to build
a simple Ruby program,
0:00
that calculates the average
of some numbers.
0:02
Here's my solution.
0:04
It's okay if yours is slightly different,
but if you see something interesting in my
0:05
code, you should consider borrowing
it to improve your own program.
0:09
Okay, so to calculate an average, we need
to add the four values in the A, B, C and
0:13
D variables together, and then divide
by 4 that's the total number of values.
0:18
Then we need to print the result out.
0:22
So to print it,
we're gonna need to call the puts method.
0:24
Now the first thing you might have tried
was to simply add a + b + c + d together.
0:27
And then divide the result by 4.
0:35
Unfortunately, that won't work because
0:37
what it will do is it will
add a + b + c + d / 4.
0:41
It'll divide d by 4 first and
then add it to a, b, and c,
0:47
which is not what you want.
0:50
Instead, we need to take order
of operations into account.
0:52
Ruby allows you to put math
operations within parenthesis so
0:58
that they take place first.
1:03
So by putting a + b + c
+ d in parentheses here.
1:05
And then that will perform all
those additional operations first.
1:10
Then take the results of that and
divide that by 4.
1:14
That's what we're going to want for
calculating the average.
1:17
Let's try running this again.
1:19
Oops, didn't save my work first.
1:23
One second.
1:25
Okay, there we go.
1:28
We're closer to what we want,
we got the number 8.
1:30
However, as I mentioned
here in the comments,
1:32
if you get 8 its because
we're dividing by a fixnum.
1:35
And unfortunately,
if you divide a fixnum by a fixnum,
1:39
ruby will truncate any fractional value
from the number to get fixnum result.
1:43
So what we need is we need to turn
one of these numbers into a float so
1:49
that we get a float result.
1:53
To convert it to a float that's as simple
as adding a decimal on to the end.
1:55
So we'll take this 4 and
turn it into a 4.0.
1:58
That way it doesn't matter even
after the results of this addition
2:01
here is a fixed number the results of
this the vision will still be a float.
2:06
And that way our number
won't get truncated.
2:11
So let's save this, run it again.
2:13
Okay, and now we're getting
the result that we expect, 8.5.
2:17
Now for the extra credit.
2:23
So we said that we could prompt
the user to enter values for these four
2:25
variables by calling gets and that we
would get a string value from gets.
2:31
So in order to convert
that to a numeric value,
2:36
we'll need to call to_f
on the value in gets.
2:40
So let's make that change
up here real quick.
2:44
We'll say, First we'll need to
print a prompt for the users.
2:47
So we'll say puts "Please
enter four numbers".
2:53
And now we'll say gets.to_f and
3:01
that will convert the string
that we get back from gets to
3:05
a float number which it will then
be stored in the a variable.
3:09
And then we'll just do the same for
these four remaining lines so
3:15
I'll just copy and paste.
3:18
Okay there we go we should now have user
entry stored in those four variables and
3:22
then will calculate an average
of those user entries.
3:28
So let's try running our program again
please and her phone numbers and
3:32
we'll just do the same ones we
did previously 12, 7, 5, and 10.
3:37
And we get a result of of 8.5.
3:41
Now lets try averaging lets say, 2, 2,
3:46
4 and 5, and we get an average of 3.25.
3:50
So not only is our average working,
3:55
we seem to be able to accept
input from the user as well.
3:57
I hope you gotten some good review
practice, see the teachers notes for
4:01
some other experiment you might trying.
4:04
Have fun.
4:06